SeaweedFS's S3 API gateway and Iceberg REST catalog gateway use routers configured with path cleaning disabled, allowing '..' segments in URLs to survive routing. This enables requests like GET /bucket-A/../evil-bucket/key to be interpreted as accessing 'evil-bucket' instead of 'bucket-A'. The captured object key is joined into a filer path where '..' collapses to the target bucket, bypassing bucket isolation. With authentication disabled, this allows direct cross-bucket access. With authentication enabled, IAM policies are evaluated against the original bucket name, but the actual I/O is performed on the traversed bucket, causing an authorization confused-deputy issue. The vulnerability affects all SeaweedFS releases prior to 4.30 and is patched in 4.30 by adding validation middleware that rejects path variables containing traversal segments or invalid characters.

This vulnerability allows unauthorized cross-bucket read and write operations. Without authentication, attackers can directly access and modify objects in any bucket by exploiting path traversal. With authentication enabled, attackers authorized for one bucket can access objects in other buckets they are not authorized for, breaking tenant isolation and potentially exposing sensitive data or allowing unauthorized data manipulation.

Upgrade SeaweedFS to version 4.30 or later, which includes a fix that adds validation middleware rejecting path variables containing '..' or '.' segments, NUL bytes, embedded slashes/backslashes in single-segment slots, or empty values. For environments unable to upgrade immediately, deploy a reverse proxy in front of the gateway to normalize request paths and reject requests containing '..', '%2e%2e', or backslash sequences. Do not rely on deployments with authentication disabled for protection, as this removes the only remaining barrier.